Find starting and ending indices of list chunks satisfying given condition

I am trying to find the start and stop indices of chunks of positive numbers in a list.

cross = [7,5,8,0,0,0,0,2,5,8,0,0,0,0,8,7,9,3,0,0,0,3,2,1,4,5,0,0,0,7,5]

For the given example input, the desired output is:

[(0, 2), (7, 9), (14, 17), (21, 25), (29, 30)]

Solution

How about using some flags to track where you are in the checking process and some variables to hold historical info?

This is not super elegant code but it is fairly simple to understand I think and fairly robust for the use case you gave.

My code

cross = [7,5,8,0,0,0,0,2,5,8,0,0,0,0,8,7,9,3,0,0,0,3,2,1,4,5,0,0,0,7,5] 
foundstart = False
foundend = False
startindex = 0
endindex = 0
for i in range(0, len(cross)):
    if cross[i] != 0:
        if not foundstart:
            foundstart = True
            startindex = i
    else:
        if foundstart:
            foundend = True
            endindex = i - 1

    if foundend:
        print(startindex, endindex)
        foundstart = False
        foundend = False
        startindex = 0
        endindex = 0

if foundstart:
    print(startindex, len(cross)-1)

Output